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What are the two criteria that classify the ways that signals are transmitted between animal cells?
- type of secreting cell
- route taken by the signal in reaching its target
cell produces signal, which travels through the blood, makes it to target cells, and those with receptor can respond
signals released to neighboring cells, only those with receptors can respond
specialized neurosecretory cells secrete neurohormones that travel to target cells via the bloodstream
the same cell that produces the signal also has a receptor for that signal
When is paracrine signaling important?
when tissues close to each other need to interact
Example of Autocrine Signaling
tumor, produces signal for the tumor itself to keep growing
Main difference between Neuroendocrine & Endocrine/Paracrine Signaling?
- Neuroendocrine- cell that secretes signal is a neuron
- In endocrine/paracrine- regular cell secretes the signal
What are pheromones?
chemicals that allow members of the same species to send signals to each other
Functions of pheromones
- marking trails leading to food
- defining territories
- warning of predators
- attracting potential mates
Endocrine vs. Exocrine glands
- endocrine- secretes stuff inside the body, secrete hormones directly into surrounding fluid
- exocrine- secretes stuff outside the body, have ducts which secrete substances onto body surfaces or into cavities
The 3 classes of hormones
- steroid hormones
Water-Soluble Hormones vs. Lipid-Soluble Hormones
- Water — can easily travel through bloodstream but has harder time entering/exiting the membrane
- Lipid — no problem exiting the membrane of producing cel, but cannot easily travel through the blood by itself
Pathway of a Lipid-Soluble Hormone
- Leaves membrane
- Binds to carrier protein in the blood to travel through bloodstream
- Can easily cross membrane when it reaches target cell
- Receptor is more likely to be inside (intracellular) because it can cross the membrane
- Receptor usually tells the cell what to do because it is already inside
Pathway of a Water-Soluble Hormone
- actively secreted through a vesicle
- easily travels through bloodstream on its own
- stays outside membrane because it cannot pass through
- needs a receptor on the membrane
- Receptor activates signal transduction pathway to deliver signal to the nucleus
Negative Feedback Loop
inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity
Positive Feedback Loop
reinforces a stimulus to produce an even greater response
What role does the hypothalamus play in endocrine regulation
receives info from the nervous system and initiates response through the endocrine system
Where is the pituitary gland located?
Attached to the hypothalamus
What are the two hormones released by the posterior pituitary?
- Oxytocin- regulates milk secretion by the mammary glands
- Antidiuretic hormone- regulates physiology and behavior
What does the ADH target?
What type of signaling does the Antidiuretic hormone employ?
Neuroendocrine signaling because neuron releases information into the bloodstream
How does anterior pituitary work?
- neurosecretory cells of the hypothalamus send signals to anterior pituitary
- Which travels through bloodstream for some distance and target the anterior pituitary, which responds by making more hormones
What is a hormone cascade pathway?
a hormone can stimulate the release of a series of other hormones, the last of which activates a non endocrine target cell
Overview of thyroid hormone being released through a hormone cascade pathway
Hypothalamus secretes a hormone, which causes anterior pituitary to produce another hormone, which causes thyroid gland to make another hormone and fix the problem
Disorders of thyroid function?
- Hypothyroidism: too little thyroid function, can produce symptoms such as weight gain, lethargy, cold intolerance
- Hyperthyroidism: excessive production of thyroid hormone, can lead to high temperate, sweating, weight loss, irritability, and high blood pressure
How can malnutrition alter thyroid function?
insufficient dietary iodine leads to an enlarged thyroid gland (goiter)
Where are the adrenal glands located?
adjacent to the kidneys
Each adrenal gland consists of two glands:
- adrenal medulla (inner portion)
- adrenal cortex (outer portion)
What does the adrenal medulla secrete?
- epinephrine (adrenaline)
- norepinephrine (noradrenaline)
What are the catecholamines secreted in response to? & what do they mediate?
- in response to stress-activated impulses from the nervous system
- They mediate various fight or flight responses
How is adrenal medulla helpful in fight-or-flight response?
- Secretes adrenaline
- which generates sugar, increasing blood pressure and increasing metabolic rate
- gets you ready to make response
What do epinephrine and norepinephrine do? (3)
- trigger release of glucose and fatty acids
- increase oxygen delivery to body cells
- direct blood towards heart, brain, and muscles
- direct blood away from skin, digestive system, and kidneys
The release of epinephrine and norepinephrine occurs in response to ________
involuntary nerve signals
What does the adrenal cortex release?
a family of steroids called corticosteroids
Humans produce two types of corticosteroids
glucocorticoids and mineralocorticoids
What are corticosteroids triggered by?
by a hormone cascade pathway via the hypothalamus and anterior pituitary
What do glucocorticoids do? (ex.)
- influence glucose metabolism and the immune system
- example: cortisol
What do mineralocorticoids do? (ex.)
- affect salt and water balance
- example: aldosterone
What does aldosterone control?
water and solute balance
Long-Term Stress Response
Hypothalamus releases hormone (ACTH), goes through blood, targets adrenal gland, which secretes mineralocorticoids and glucocorticoids that can respond to the stress
Short-term Stress Response
Hypothalamus signals adrenal medulla through nerve impulses, which then in turn secretes epinephrine and norepinephrine
How does negative feedback loop come into play in diabetes mellitus?
- Negative feedback loop is broke
- blood glucose level doesn’t drop, it stays high
Why is the urine sweet in diabetes mellitus?
because blood glucose levels are very high and glucose makes the urine sweet
Sets of hormones from the hypothalamus, the anterior pituitary, and a target endocrine gland are often organized into a
hormone cascade pathway.
The anterior pituitary hormones in these hormone cascade pathways are called
Function of thyroid hormone
- regulates bioenergetics
- helps maintain normal blood pressure, heart rate, and muscle tone
- and regulates digestive and reproductive functions.
Describe the process of thyroid regulation
- If the level of thyroid hormone in the blood drops, the hypothalamus responds by initiating a hormone cascade pathway
- The hypothalamus secretes thyrotropin-releasing hormone (TRH), causing the anterior pituitary to secrete a tropic hormone known as either thyroid-stimulating hormone (TSH) or thyrotropin
- TSH stimulates release of thyroid hormone by the thyroid gland, an organ in the neck consisting of two lobes on the ventral surface of the trachea.
- As thyroid hormone accumulates, it increases metabolic rate, while also initiating negative feedback that prevents its overproduction.